Summary: Serializability as an isolation criterion, though well suitable for traditional transactions, would overly restrict the concurrency of long lasting activities such as workflows. By using semantic information it is possible to weaken, or give up altogether, the serializability criterion and yet ensure workflow execution correctness. The problem, however, is that the use of semantic information in concurrency control makes the specification as well as the management of workflows more complex. We alleviate this problem by introducing self-isolating workflows, which set and unset consistency constraints in the database in a way analogous to the way in which traditional transactions obtain and release locks. The advantages of using consistency constraints in workflow isolation are twofold. First, the expression power of consistency constraints in a database query language is high, which in turn increases the potential degree of concurrency. Second, workflow concurrency control can be implemented by using the services of the underlying database management system.